Osteoarthritis (OA) affects over half the population at some point in their lives, yet treatment options and understanding of OA remain limited, in part due to limited availability of non-invasive techniques to quantify disease progression and responses to therapies. While numerous magnetic resonance imaging (MRI) methods have been proposed for imaging OA, they all have at least one major limitation, ranging from long scan times to limited specificity. We propose a new MRI technique called quantitative double-echo in steady-state (qDESS) imaging that simultaneously offers 3D morphologic and functional imaging of the entire knee, including water diffusion and rapid relaxometry measurements. This project aims to fully develop qDESS so that it may be widely used, then to assess the value of quantitative diffusion and relaxometry measures in cartilage and menisci to detect early and temporal changes. Our specific aims are (1) to develop a robust scanning sequence and accompanying post-processing methods to obtain high-resolution 3D maps of apparent diffusion coefficient (ADC), T2 and T2* in a 10-minute scan at 3T, (2) to validate this technique with imaging of excised human samples, comparing quantitative imaging parameters with biochemical, histological and mechanical metrics in cartilage and menisci to determine sensitivity to tissue degeneration, and (3) to validate the ability of qDESS to detect changes over time in the knees of subjects at risk of developing OA following anterior cruciate ligament (ACL) tears. The innovation of this work lies in the development of a clinically feasible technique that simultaneously offers (1) morphologic images that can potentially be used for whole-knee scoring and radiologic assessment and (2) quantitative parameters in both cartilage and meniscus including volume and thickness measurements, T2 and T2* maps and ADC maps, and (3) a non-contrast-enhanced method to assess synovitis. The significance of this proposal is to offer a widely available, quantitatively validated 10-minute imaging method that makes comprehensive routine study of early osteoarthritis feasible in both research and clinical MRI exams.